1. Field of the Invention
The present invention relates to an apparatus and a method for controlling the operation of an air conditioner for cooling or heating indoor air.
2. Description of the Related Art
Generally, an air conditioner is an appliance for cooling or heating an indoor space, such as a residential space, a restaurant, an office room, or etc. The air conditioner comprises a compressor, a condenser, an expansion device, and an evaporator. The compressor serves to compress a refrigerant into a high-temperature and high-pressure gaseous state. The condenser serves to condense the refrigerant passing through the compressor into a high-temperature and high-pressure liquid state. The expansion device serves to decompress the refrigerant passing through the condenser into a low-temperature and low-pressure liquid state. The evaporator serves to evaporate the refrigerant passing through the expansion device into a low-temperature and low-pressure gaseous state. The compressor, the condenser, the expansion device, and the evaporator are connected through a refrigerant pipe.
A heat pump-type air conditioner further comprises a direction change valve, such as a 3-way valve or a 4-way valve, adapted to change the flow direction of the refrigerant based on a cooling/heating function, thereby being selectively operated in a cooling or heating mode.
In the cooling mode of the air conditioner, an outdoor heat exchanger functions as the condenser, and an indoor heat exchanger functions as the evaporator. On the other hand, in the heating mode of the air conditioner, the outdoor heat exchanger functions as the evaporator, and the indoor heat exchanger functions as the condenser.
In the cooling mode, the air conditioner allows indoor air to pass through the indoor heat exchanger functioning as the evaporator, thereby discharging cold air to the room. In the heating mode, the air conditioner allows indoor air to pass through the indoor heat exchanger functioning as the condenser, thereby discharging warm air to the room.
A recently developed air conditioner employs a plurality of compressors having different capacities so that the plural compressors are simultaneously or selectively operated in accordance with a cooling or heating load. Accordingly, it is possible to properly cope with the variation of the cooling or heating load, thereby optimizing the cooling or heating efficiency of the air conditioner.
Generally, a capillary tube or an electronic expansion valve may be used as the expansion device. The electronic expansion valve is mainly used as the expansion device for adjusting the flow rate of the refrigerant so that the cooling or heating capacity of the air conditioner can be variably changed.
A user selects one of the cooling and heating modes of the air conditioner, and sets a desirable target temperature. Then, a cooling or heating load to be eliminated is determined by the difference between the target temperature and a current room temperature. Under the condition in which the flow rate of the refrigerant is controlled according to the determined cooling or heating load, the refrigerant passes through the compressors, the condenser, the electronic expansion valve and the evaporator sequentially. Thereby, the air conditioner is operated in the cooling or heating mode.
The conventional air conditioner has recently become large in size, thus requiring a plurality of compressors. One or more compressors of the above plural compressors are selectively operated according to a cooling or heating load to be eliminated. The total refrigerant compression capacity of the operating compressors is variably changed according to the variation of the cooling or heating load, but the flow rate of the refrigerant set according to an initial cooling or heating load is fixed.
Accordingly, in case that the circulating rate of the refrigerant is smaller than the total refrigerant compression capacity of the operating compressors, i.e., the rate of the refrigerant compressed by the operating compressors, the operating compressors are overheated. On the other hand, in case that the circulating rate of the refrigerant is larger than the rate of the refrigerant compressed by the operating compressors, the refrigerant is introduced into the compressors, thus causing failure of the compressors. Further, these cases cause an air conditioning system using the air conditioner to be in an abnormal state, thereby lowering the efficiency of the air conditioning system.
Therefore, the present invention has been made in view of the above problems, and it is an object of the present invention to provide an apparatus for controlling the operation of an air conditioner, in which one or more compressors are operated according to a cooling or heating load to be eliminated and the flow rate of a refrigerant is controlled, so that an air conditioning system using the apparatus is stably operated.
It is another object of the present invention to provide a method for controlling the operation of an air conditioner in which one or more compressors are operated according to the variation of a cooling or heating load and the flow rate of a refrigerant is controlled within a set range based on the total refrigerant compression capacity of the operating compressors, thus rapidly coping with the variation of the cooling or heating load and improving a cooling or heating efficiency.
In accordance with one aspect of the present invention, the above and other objects can be accomplished by the provision of an apparatus for controlling an operation of an air conditioner having a plurality of compressors simultaneously or selectively operated according to a cooling/heating load for compressing a refrigerant so that the total refrigerant compression capacity of the operating compressors are variably changed, a condenser for condensing the refrigerant compressed by the compressors by heat-exchanging the refrigerant with air, an electronic expansion valve for expanding the refrigerant condensed by the condenser by decompressing the refrigerant, an evaporator for evaporating the refrigerant expanded by the electronic expansion valve by heat-exchanging the refrigerant with air, and a refrigerant pipe for connecting the compressors, the condenser, the electronic expansion valve, and the evaporator, comprising: a first temperature sensor, installed at the refrigerant pipe connected to the condenser, for measuring the temperature of the refrigerant; a second temperature sensor, installed at the refrigerant pipe connected to the evaporator, for measuring the temperature of the refrigerant; a third temperature sensor, installed at the refrigerant pipe connected to the compressors, for measuring the temperature of the refrigerant sucked into or discharged from the compressors; and a control unit for calculating the cooling/heating load according to the temperatures of the refrigerant measured by the first, second and third temperature sensors and a desirable target temperature set by a user, controlling the operation of the plural compressors according to the cooling/heating load, calculating minimum and maximum values of an opening degree of the electronic expansion valve according to the total refrigerant compression capacity of operating compressors selected from the plural compressors, and controlling the opening degree of the electronic expansion valve between the minimum and maximum values.
Preferably, the plural compressors may include first and second compressors having different refrigerant compression capacities, and the refrigerant compression capacity of the first compressor may be larger than that of the second compressor.
Further, preferably, the control unit may operate both of the first and second compressors simultaneously or operates only the second compressor, according to the cooling load, in a cooling mode, or operate both of the first and second compressors simultaneously or operates only the first compressor, according to the heating load, in a heating mode.
Preferably, the apparatus may further comprise an outdoor temperature sensor installed at one side of an outdoor heat exchanger functioning as the condenser or the evaporator.
Further, preferably, the control unit may calculate the minimum and maximum values of the electronic expansion valve in consideration of the outdoor temperature measured by the outdoor temperature sensor.
In accordance with another aspect of the present invention, there is provided a method for controlling an operation of an air conditioner comprising the steps of: (a) operating one or more of a plurality of compressors so that the total refrigerant compression capacity of the operating compressors is variably changed according to a cooling/heating load; (b) setting minimum and maximum values of an opening degree of an electronic expansion valve according to the total refrigerant compression capacity of the operating compressors in a cooling or heating mode; and (c) controlling an opening degree of the electronic expansion valve between the set minimum and maximum values.
Preferably, the step (a) may include the step of determining whether first and second compressors having different refrigerant compression capacities are simultaneously or selectively operated.
More preferably, the refrigerant compression capacity of the first compressor is larger than that of the second compressor.
Preferably, the first and second compressors may be simultaneously operated or only the second compressor is operated, according to the cooling load, at the step (a) in a cooling mode, or the first and second compressors may be simultaneously operated or only the first compressor is operated, according to the heating load, at the step (a) in a heating mode.
More preferably, the step (b) may include the step of variably setting the minimum and maximum values of the electronic expansion valve in accordance with the outdoor temperature, in case that both of the first and the second compressors are simultaneously operated in the cooling mode.
Preferably, the minimum and maximum values may be set so that a passage through the electronic expansion valve is opened in the range of 46xcx9c64% at the step (b), when the outdoor temperature is more than a set value, in case that both of the first and the second compressors are simultaneously operated in the cooling mode. The minimum and maximum values may be set so that a passage through the electronic expansion valve is opened in the range of 32xcx9c64% at the step (b), when the outdoor temperature is not more than a set value, in case that both of the first and the second compressors are simultaneously operated in the cooling mode.
And, preferably, the minimum and maximum values may be set so that a passage through the electronic expansion valve is opened in the range of 18xcx9c38% at the step (b), in case that only the second compressor is operated in the cooling mode.
Further, preferably, the minimum and maximum values may be set so that a passage through the electronic expansion valve is opened in the range of 16xcx9c50% at the step (b), in case that both of the first and the second compressors are simultaneously operated in the heating mode.
Moreover, preferably, the minimum and maximum values may be set so that a passage through the electronic expansion valve is opened in the range of 12xcx9c44% at the step (b), in case that only the first compressor is operated in the heating mode.